So, I have mounted the PowerBlock and I have tested it for some days. It works almost as expected, spordically it shows unexpected behaviour. I will create a separate thread explaining my observations.
Anyway, thanks for supplying me with a replacement device.
It should always be possible to use the ControlBlock together with any USB controller. You would just need to run the input configuration for each device on EmulationStation. All controller types should be recognised and working afterwards.
Regarding your question about the need for an additional keyboard: What you would need to do is to configure the emulators such that you have full control with your arcade / gamepad controls only. That should be possible.
That looks like it would do the trick, but it also looks like a daunting endeavor. I'd have to modify the design to work in my case with a full size NES case. All those mini jump wires between contacts is going to suck for me too. Plus I have no idea what those other parts (diode, resistor, capacitor, etc) are used for. I wish I knew more about electronic circuits. That's why I liked the Mausberry circuit so much, plug in, put the wires where they need to go, and you're done (after getting the script obviously). The PowerBlock was useful too because you just attach it to the GPIO pins. I still think doing something like the Mausberry would work best, but I'm not sure if they can support the amps. Waiting for them to reply.